Many kinds of quick charge batteries such as Ni-Cd battery which belongs to alkaline batteries, have been introduced. Because such batteries need relatively short charge time, they are suitable to be used as power sources of electronic instruments and lots of battery charging circuits, which can charge such batteries very quickly, have been adopted. However, these batteries are apt to be overcharged because most of the conventional charging circuits lack the protecting means which can prevent the batteries from being overcharged. Furthermore, the batteries overcharged as such can destroy the circuits and instruments for which they are used as the power sources.